The invention relates to a method and apparatus which is particularly useful for regulating the individual shares of gaseous constituents of oxygen, nitrogen, carbon dioxide and water in reaction processes in the metallurgical field. Such methods generally aim at savings in energy, and especially savings with respect to the use of expensive means for transporting energy supplies. The reasons for this may be availability, dependence on importation, environmental factors, potential risks during conveyance, and last but not least prices and costs of certain fuels. Accordingly, such methods also aim at the utilization of gaseous and liquid fuels which question the economy of metal extraction, particularly crude iron and/or steel production in metallurgical processes where high temperatures are involved.
In the reduction of ore approximately 3000 normal or standard cubic meters of air are required for the combustion of one ton of coke. The air quantity actually to be delivered is still higher by about 25% due to atmospheric moisture, and due to leaks in pipes and air heaters (e.g. in blast heaters in blast furnaces). In order to save fuel, such as coke, the air is heated to a maximum of 1,300.degree. C. in air heaters. In order to heat the air, the blast furnace gas escaping from the metallurgical furnace is used with a coke gas additive which is burned in the air heater, thereby heating latticed refractory stones in the interior of the air heater to a maximum of 1,550.degree. C. After the heating period, the gas burner is switched off, and the cold air, which is produced in blower engines at higher pressures, is blown through the hot latticed masonry of the air heater. The hot stones heat the air, which is then injected, into the blast furnace, via the hot blast annular conduit and the blast pipes. Two such blast heaters alternate in heat and blast periods. About 66% of the total energy of a metallurgical plant are used in the extraction of crude iron in blast furnaces. The coke consumption in the Federal Republic of Germany alone in the year of 1975 amounted to about 500 kilograms per ton of crude iron. In addition, about 60 kg of heavy diesel oil per ton of crude iron were injected.
The blast furnace gas at the blast furnace, however, is a gas low in calorific value (3,140 to 3,560 kJ/m.sup.3). This disadvantage may be compensated for in order to obtain higher flame temperatures, usually by adding heavy gases, such as coke furnace gas. Other auxiliary means to obtain higher flame temperatures exist in the preheating of gas and/or combustion air. It has also been suggested to decrease the inert gas quantities in the combustion air (particularly nitrogen) by adding oxygen in order to save fuel and at the same time increase the output of the blast furnace.
The oxygen added previously in the blast furnace originates mainly with the low temperature distillation of atmospheric air, for which special oxygen extraction plants are required in metallurgical plants. On the other hand, metallurgical plants may also be connected to extensive oxygen conduit systems, which join the individual oxygen consumption points in the metallurgical plant with far removed oxygen extraction plants.
The mere addition of oxygen to the combustion air and/or to gases low in calorific value, in particular blast furnace gases, is therefore not only relatively involved, but, in addition, it does not solve the problem of the other attendant gaseous constituents present, such as for example the inert gases, and particularly nitrogen which has to be carried as ballast in the metallurgical process. The supply of pure oxygen is, furthermore, unable to solve the problem of the carbon dioxide and the water vapor in the combustion air.
The present invention is a new method and apparatus for regulating the individual quantities of combustion air constituents, including the content of oxygen, nitrogen, carbon dioxide, and water in reaction processes in metallurgy, making it possible to individually determine a desired composition of the combustion gas according to calorific value, temperature and combustion gas volumes required for any type of process. This is achieved by supplying the reduction processes and/or oxidation processes with a controllable quantity of air, where the oxygen share has previously been increased in relation to the existing oxygen share of the inlet air, by continuously absorbing by molecular screening and/or straining in a flow of nitrogen, carbon dioxide and water molecules in substances forming crystal lattices. This method has the advantage of, simultaneously with an enrichment of the combustion air in oxygen, reducing the share of gases not participating in the combustion, and even inhibiting the latter. Thus, the share of ballast and unnecessary gases which is often found to be disadvantageous in reduction processes and oxidation processes, is lowered considerably.
Another advantage is that this share is controllable depending upon the temperature level to be set. For use as the molecular screen, such substances are suitable which are able to bind larger quantities of water in the crystal lattice, and which may be removed continuously by simple heating without collapse of the crystal lattice. In an atmosphere containing water vapor, such drained crystals may again absorb water or, in its place, sulfur hydrogen, sulfur carbon, nitrogen, carbon dioxide, and other molecules. Such crystal lattices are known under the name of Zeolite. Since the natural Zeolites are not adequate for this purpose, synthetic Zeolites have been manufactured for about 50 years which fulfill the practical demands.
The special advantage of the method described lies, in short, in the use of substances forming crystal lattices, which are of corresponding pore sizes and crystal lattice structures where foreign molecules with smaller diameter than the hollow spaces of the lattice may be absorbed. The other advantage lies in the typically metallurgical application. For the latter, the method of the invention presents opportunities to introduce gases lower in ballast into reduction or oxidation processes, to introduce gases which are more intensly reactive, to completely utilize generally unused waste heat of reduction or oxidation processes, and to regenerate substances forming crystal lattices and pores. Furthermore, the invention produces far drier combustion gases, and finally provides for the carrying out of more intensive reduction and oxidation processes by producing oxygen-enriched air. The last advantage serves to intensify the processes, thereby increasing the output of metallurgical furnaces and combustion processes. One of these advantages, therefore, consists in obtaining higher temperatures--as far as required--in reduction and oxidation processes.
According to the invention, it is advantageous for the controlled air in quantity to be fed through a Zeolite molecular screen consisting of crystalline metal alumino-silicates. Such zeolite molecular screens are in themselves known. Their suitability for absorbing certain constituents attendant with the supply air which are undesirable in certain quantities in reduction processes and/or oxidation processes, has so far been overlooked. The method of the invention is furthermore improved in that the zeolite molecular screen is regenerated with air heated to temperature between 200.degree. C. and 300.degree. C., for purging nitrogen, carbon dioxide and water contents by molecular displacement in an air flow in opposite direction to the previously set up operational flow. It is, further, advantageous to carry out regeneration of the molecular screen in an alternating temperature method by periodic heating of the molecular screen. Also, regeneration of the molecular screen can be done by alternating pressure application by periodic lowering of the pressure of the air flow at a constant temperature.
As a further feature of the invention, provision is now made that the air enriched with oxygen is supplied to reduction processes in shaft furnaces (e.g. in a blast furnace) for the ore reduction or oxidation processes and/or reduction processes and/or smelting processes in steel mill converters, cupola furnaces and/or electro-furnaces for the refining of crude iron and/or smelting of metal scrap, iron sponge and/or for the extraction of nonferrous metals, as well as hot and glow furnaces for heating and heat treatment of metals. Another use of the method of the invention is that the air enriched with oxygen may be burned together with blast furnace gas in the combustion chamber of a blast heater, so that there is a saving of coke gas. Also, another use of the invention is that the oxygen-enriched air may be heated together with fresh air in a blast furnace blast heater.
The apparatus of the invention is formed so that a metallurgical furnace is preceded by several containers with molecular screen substances, which alternately may be connected to an air supply, and which are, furthermore, alternately connectable to a source of heat coupled with a cold air supply. The alternating connection is of advantage inasmuch as the molecular screens must be relieved from time to time from accumulated materials. With at least two containers with molecular screen substances there is always one ready for operation. During the operation period of one of the molecular screen containers, the other container or containers may be regenerated. To this end, the respective molecular screen containers are mounted to allow air flow in opposite directions depending upon whether they are receiving hot air or fresh air. In principle, the undesirable constituents attending the air, which are not to participate in the respective reaction, may be purged from the molecular screen container. To this end, it is useful that each molecular screen container be provided with an escape valve for nitrogen, carbon dioxide and water.
In a metallurgical operation where the metallurgical furnace operates as consumer and heat accumulates at the same time, the apparatus as per invention is suitably formed so that at least three molecular screen containers are provided with alternate connections between each other while being coordinated with a metallurgical furnace and/or combustion shaft. Suitably, the heat source for the regeneration circuit of the molecular screen containers consists of a tube recuperator. For an extensive run of the processes in the molecular screen crystals, it is, furthermore, important that the molecular screen containers contain a heat-insulated steel jacket.
An example of the apparatus of the invention is shown in the drawing, wherein an example of the apparatus and the method of the invention is illustrated.